The long range objectives are to identify the connections and neurotransmitter/neuromodulator substances of neurons located in the medullary raphe nuclei. These studies would provide a foundation of the anatomical circuitry necessasry for the future development of pharmacological and behavioral appraoches to better understand the influences of the raphe nuclei in regards to their regulation of sensory, motor and autonomic functions, as well as, sleep-arousal mechanisms and affective disorders. The experimental neuroanatomical studies of the present proposal will employ various axonal tracing techniques combined with immunocytochemistry to define the serotonergic, peptidergic and cholinergic connections of the raphe nuclei. The experiments are divided into four main parts: (a) transmitter-specific neurons; (b) transmitter-specific efferent pathways; (c) transmitter-specific terminations and (d) collateralization of raphe neurons.